A nitrogen-doped carbon-based composite electrode material, a preparation method therefor, and an application thereof

Abstract

This invention provides a nitrogen-doped carbon-based composite electrode material, its preparation method, and its application. The method includes: impregnating a melamine sponge in a suspension formed by mixing activated carbon, a conductive agent, a binder, and a solvent; drying the impregnated melamine sponge and calcining it in an oxygen-free atmosphere; and cooling to obtain the nitrogen-doped carbon-based composite electrode material. The nitrogen-doped carbon-based composite electrode material of this invention is prepared by this method. This invention also provides the application of this nitrogen-doped carbon-based composite electrode material as a self-supporting electrode in energy storage and conversion devices. The technical solution of this invention can improve the nitrogen doping level of the electrode material, achieve the self-supporting function of the electrode, and improve the mass transfer efficiency of the electrode.

Description

Technical Field

[0001] This invention relates to a nitrogen-doped carbon-based composite electrode material, its preparation method, and its application, belonging to the field of carbon materials technology. Background Technology

[0002] Self-supported electrodes, which are electrodes that directly function as electrode materials without the need for additional current collectors or electrode assembly processes, possess excellent mechanical properties and higher mass transfer efficiency. They can be freely cut to achieve electrode fabrication of different sizes and scales, overcoming the shortcomings of traditional powder electrode materials in these aspects. They can be widely used in flexible electrodes, compressible electrodes, and electrodes for capacitor deionization devices in energy storage devices such as supercapacitors and lithium-sulfur batteries, and have become a research hotspot in recent years. Currently, self-supported electrodes are mostly found in thin film and porous foam forms. On the other hand, nitrogen doping has been proven to be an important means of improving electrode capacity and electrode interface properties (such as hydrophilicity) (J. Mater. Chem. A, 2018, 6, 17730). This can be achieved through material post-processing or in-situ doping using a one-step carbonization of nitrogen-rich precursors.

[0003] Melamine sponge, a nitrogen-rich material with a three-dimensional porous structure (high porosity, >98%), is an important raw material for the preparation of nitrogen-doped self-supporting electrodes.

[0004] CN114053996A discloses a one-piece molded nitrogen-containing bulk porous carbon material, its preparation method, and its application. This method involves immersing a melamine sponge in a glucose solution, freeze-drying it, carbonizing it, and then activating it with carbon dioxide to prepare a one-piece molded nitrogen-containing bulk porous carbon material. However, this method uses a solution impregnation method, resulting in a low actual glucose load after solution drying, and the glucose carbonization yield is only 30%, leading to a low overall density of the prepared material. Furthermore, while the post-activation treatment increases the specific surface area of ​​the material, it further breaks down the carbonized melamine framework, significantly reducing its mechanical strength.

[0005] CN113223862A discloses an activated sponge capacitor material, its preparation method, and its application. The method involves carbonizing melamine sponge, impregnating it with a dopamine-graphene oxide aqueous solution, drying it, and then carbonizing and activating it to obtain a nitrogen-doped electrode. However, the dopamine and graphene oxide used in this method are both high-value raw materials, resulting in high production costs and a low specific surface area of ​​the obtained electrode.

[0006] CN108074751A discloses a flexible three-dimensional porous carbon material, its preparation method, and its application. This method involves dissolving coal tar pitch and potassium hydroxide, impregnating the resulting material with melamine sponge, and then carbonizing and activating it to obtain a nitrogen-doped flexible three-dimensional porous electrode material. However, the potassium hydroxide used in this method has extremely strong etching properties; although the obtained electrode material has a large specific surface area, the mechanical strength of the electrode is severely compromised.

[0007] CN105826562A discloses a nitrogen-doped carbon flexible paper, its preparation method, and its application. This method involves oxidizing and compressing melamine sponge to obtain a flexible nitrogen-doped porous material. While the preparation process is simple, the specific surface area of ​​the prepared material is too low to be suitable for energy storage applications.

[0008] The paper "The Carbonization Temperature Effect on the Electrochemical Performance of Nitrogen-Doped Carbon Monoliths" (J. Electacta. 2017.05.016) describes the direct carbonization of melamine sponge for use as a capacitor electrode. However, the specific surface area of ​​this electrode is too low (<30 m²). 2 / g), which has poor performance in practical energy storage applications.

[0009] Developing a novel nitrogen-doped carbon-based composite electrode material and its preparation method remains one of the urgent problems to be solved in this field. Summary of the Invention

[0010] To address the aforementioned technical problems, the present invention aims to provide a nitrogen-doped carbon-based composite electrode material, its preparation method, and its applications. The technical solution of the present invention can improve the nitrogen doping level of the electrode material, achieve the self-supporting function of the electrode, and improve the mass transfer efficiency of the electrode.

[0011] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a nitrogen-doped carbon-based composite electrode material, comprising the following steps:

[0012] Melamine sponge was impregnated in a suspension formed by a mixture of activated carbon, conductive agent, binder and solvent, and the impregnated melamine sponge was dried to obtain a composite precursor; the composite precursor was calcined in an oxygen-free atmosphere and cooled to obtain the nitrogen-doped carbon-based composite electrode material.

[0013] Of which, based on the total mass of activated carbon, conductive agent and binder as 100%, the amount of activated carbon is 50-93%, the amount of conductive agent is 2-30%, and the amount of binder is 5-20%.

[0014] In the above preparation method, preferably, the density of the melamine sponge is 4-20 kg / m³. 3 The open area ratio is 95-99.8%.

[0015] In the above preparation method, preferably, the specific surface area of ​​the activated carbon is 200-4000 m². 2 / g, particle size 2–100μm (based on D50 diameter), micropores with a pore size less than 2nm and a pore volume of 0.3–0.9cm³. 3 / g, total pore volume is 0.3~1.5cm³ 3 / g. More preferably, the specific surface area of ​​the activated carbon is 800-2000 m². 2 / g, particle size of 6–20 μm (based on D50 diameter), micropores with a pore size of less than 2 nm and a pore volume of 0.45–0.8 cm³. 3 / g, total pore volume is 0.5–1.5 cm³ 3 / g.

[0016] In the above preparation method, preferably, the conductive agent includes one or a combination of several of carbon black, graphene, and graphite.

[0017] In the above preparation method, preferably, the adhesive includes one or a combination of several of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, styrene-butadiene latex, and polyvinyl alcohol.

[0018] In the above preparation method, preferably, the solid content of the suspension is 5-50% by volume percentage.

[0019] In the above preparation method, preferably, activated carbon, conductive agent, binder and solvent are formed by uniformly mixing and dispersing a suspension, wherein the uniform mixing and dispersion method includes one or a combination of several of the following: stirring mixing, ultrasonic-assisted mixing and vacuum-assisted mixing.

[0020] In the above preparation method, preferably, the melamine sponge is impregnated in the suspension by ultrasonic-assisted impregnation.

[0021] In the above preparation method, preferably, the melamine sponge is immersed in the suspension for 2 to 30 minutes.

[0022] In the above preparation method, preferably, the mass ratio of the melamine sponge to the activated carbon in the suspension is 1:100 to 1:1000.

[0023] In the above preparation method, preferably, the mass ratio of melamine sponge to activated carbon in the composite precursor is 1:0.5 to 1:10.

[0024] In the above preparation method, preferably, controlling the calcination atmosphere to be an oxygen-free atmosphere includes: placing the composite precursor in a calcination furnace, first using a vacuum system to remove the air from the calcination furnace, and then introducing a non-oxidizing gas to completely replace the air in the pores of the composite precursor. More preferably, the non-oxidizing gas can be repeatedly introduced several times.

[0025] In the above preparation method, preferably, the non-oxidizing gas includes one or a combination of several of nitrogen, argon, carbon dioxide and helium.

[0026] In the above preparation method, preferably, no gas is introduced during the calcination process.

[0027] In the above preparation method, preferably, the constant temperature for calcination is 650-950℃, more preferably 700-900℃, and even more preferably 750-850℃.

[0028] In the above preparation method, preferably, the heating rate of calcination is 0.5-10℃ / min, more preferably 1-8℃ / min, and even more preferably 2-5℃ / min.

[0029] In the above preparation method, preferably, the calcination isothermal time is 30-180 min, more preferably 60-120 min.

[0030] The second aspect of the present invention provides a nitrogen-doped carbon-based composite electrode material, which is prepared by the above-described method for preparing nitrogen-doped carbon-based composite electrode materials.

[0031] According to a specific embodiment of the present invention, preferably, the nitrogen-doped carbon-based composite electrode material has a specific surface area of ​​500–1500 m². 2 / g, total pore volume is 0.3~1.5cm³ 3 / g, compacted density is 0.15~0.45g / cm³ 3 The nitrogen content in the nitrogen-doped carbon-based composite electrode material is 2.5% to 12% by mass.

[0032] The third aspect of the present invention provides the application of the above-mentioned nitrogen-doped carbon-based composite electrode material as a self-supporting electrode in energy storage and conversion devices.

[0033] In the above applications, preferably, the energy storage and conversion device includes one or a combination of several of the following: supercapacitors, lithium-sulfur batteries, lithium-ion batteries, sodium-ion batteries, lithium-ion capacitors, sodium-ion capacitors, potassium-ion capacitors, and capacitor deionization devices. More preferably, the energy storage and conversion device includes double-layer capacitors and / or capacitor deionization devices.

[0034] This invention provides a nitrogen-doped carbon-based composite electrode material, its preparation method, and its applications. The preparation method involves combining activated carbon, a conductive agent, and melamine sponge, followed by a one-step calcination process to obtain the composite electrode material. This invention solves the problems of cumbersome preparation steps, low nitrogen doping uniformity, insufficient mechanical strength due to post-activation treatment, and low electrode density in existing nitrogen-doped carbon-based self-supporting electrodes. This invention improves the nitrogen doping level of the electrode material, achieves self-supporting electrode functionality, and enhances the electrode's mass transfer efficiency.

[0035] The technical solution of the present invention has at least the following beneficial effects:

[0036] Beneficial effect 1: Composite electrode materials possess self-supporting properties

[0037] Traditional powdered activated carbon requires slurry preparation and coating with current collectors (such as aluminum foil, copper foil, or nickel foam) to prepare electrodes, resulting in heavier electrodes and lower electrode mass-to-capacity ratios.

[0038] This invention uses melamine sponge as a framework, anchoring / embedding activated carbon and a conductive agent within the sponge pores. The electrode material is directly prepared through a single carbonization (calcination) step. The carbonized melamine sponge possesses high mechanical strength, enabling elastic deformation of the electrode. Simultaneously, the activated carbon acts as a filler, support, and reinforcement, preventing structural fracture and failure during sponge framework deformation. The electrode material of this invention does not require an additional metal current collector, significantly improving the overall mass-to-capacity ratio of the electrode.

[0039] Beneficial effect 2: Composite electrode materials possess high energy density

[0040] The composite electrode material of the present invention has a high volume density, which can further improve the electrode volume capacity. Moreover, the electrode material of the present invention can be used directly without further activation, preventing damage to the melamine backbone structure during the activation process.

[0041] Beneficial effect 3: The composite electrode material has a high level of nitrogen doping.

[0042] In this invention, the melamine sponge serves as both a supporting framework and a nitrogen doping source for the composite electrode. During the calcination of the melamine sponge, pyrolysis generates a large amount of nitrogen-containing gas (Research on the Preparation of Carbon and Nitrogen Precursors by Melamine Pyrolysis, Master's Thesis, Yanshan University, 2004). During the heating and isothermal stages, the nitrogen-containing gas released by the melamine pyrolysis overflows onto the surface of the activated carbon and undergoes a nitrogen-carbon doping reaction at the calcination temperature. That is, at high temperature, it forms a carbon-nitrogen bond structure with carbon atoms in the pores of the activated carbon, achieving in-situ nitrogen doping of the activated carbon.

[0043] Beneficial effect 4: Improved mass transfer efficiency of composite electrode materials

[0044] Melamine sponge has an extremely high porosity, with macropores (10-100 μm). Activated carbon, on the other hand, is mainly microporous (<2 nm), with a large adsorption capacity, but low mass transfer efficiency when used alone as an electrode material (Electronic Components and Materials, 2021, 40(5):406-413). The composite electrode of this invention uses activated carbon as both a filler and adsorbent, which is the main site for ion adsorption. Melamine sponge serves as the substrate framework, uniformly bonded between the activated carbon particles. The resulting capillary action rapidly transfers ions to the surface of the activated carbon particles, improving adsorption efficiency and further enhancing the rate performance of the electrode.

[0045] In summary, the nitrogen-doped carbon-based composite electrode material and its preparation method provided by this invention can achieve beneficial effects such as improving electrode strength, increasing nitrogen doping level, and improving ion transport efficiency, thereby improving mass transfer efficiency, rather than simply being a combination of the properties of various raw materials. The nitrogen-doped carbon-based composite electrode material provided by this invention can be applied in energy storage and conversion fields involving electroadsorption, including capacitor energy storage and capacitor deionization, as well as other scenarios requiring self-supporting electrodes and nitrogen-doped electrodes, especially demonstrating better performance in double-layer capacitor electrodes and capacitor deionization device electrodes. Moreover, the nitrogen-doped carbon-based composite electrode material and its preparation method provided by this invention meet the industrial demands for low cost, uniform quality, and ease of engineering. Attached Figure Description

[0046] Figure 1 This is a process route diagram for preparing nitrogen-doped carbon-based composite electrode materials according to some specific embodiments of the present invention.

[0047] Figure 2 A photograph of the composite electrode 1 provided in Example 1.

[0048] Figure 3 A photograph illustrating the bending resistance of the composite electrode 2 provided in Example 2.

[0049] Figure 4 A photograph illustrating the compression-rebound performance of the composite electrode 2 provided in Example 2.

[0050] Figure 5 Linear cyclic voltammetry curve of the capacitor assembled with the composite electrode 1 provided in Example 1.

[0051] Figure 6 The AC impedance spectrum of the composite electrode 1 assembly provided in Example 1.

[0052] Figure 7Adsorption-desorption isotherms of the composite electrode 1 provided in Example 1 and the comparative electrode 2 provided in Comparative Example 2. Detailed Implementation

[0053] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0054] The first aspect of this invention provides a method for preparing a nitrogen-doped carbon-based composite electrode material, comprising the following steps:

[0055] Melamine sponge was impregnated in a suspension formed by a mixture of activated carbon, conductive agent, binder and solvent, and the impregnated melamine sponge was dried to obtain a composite precursor; the composite precursor was calcined in an oxygen-free atmosphere and cooled to obtain the nitrogen-doped carbon-based composite electrode material.

[0056] Of which, based on the total mass of activated carbon, conductive agent and binder as 100%, the amount of activated carbon is 50-93%, the amount of conductive agent is 2-30%, and the amount of binder is 5-20%.

[0057] In some preferred embodiments of the present invention, such as Figure 1 As shown, the preparation method of the nitrogen-doped carbon-based composite electrode material includes the following steps:

[0058] (1) Preparation of suspension: Activated carbon, conductive agent, binder and solvent are uniformly mixed and dispersed to form a suspension;

[0059] (2) Impregnation: The melamine sponge is completely impregnated in the suspension to obtain the impregnated sponge;

[0060] (3) Drying: The impregnated sponge is dried to remove the solvent and obtain the composite precursor;

[0061] (4) Carbonization: The composite precursor is calcined in an oxygen-free atmosphere and cooled to obtain the nitrogen-doped carbon-based composite electrode material.

[0062] In some specific embodiments, the density of the melamine sponge is 4–20 kg / m³. 3 The porosity is 95-99.8%, and the average pore size is 10-100 μm.

[0063] In some specific embodiments, the melamine sponge can be washed, dried, and cut before impregnation. For example, in some embodiments of the present invention, the melamine sponge is washed to remove surface impurities; the washing solvent may include deionized water and / or ethanol, etc.; the drying temperature after washing can be conventionally selected by those skilled in the art; subsequently, the melamine sponge is cut to a certain size, for example, cut into melamine sponges of 2.0cm × 2.0cm × 0.5cm (length × width × height) for later use.

[0064] In some specific embodiments, the activated carbon may include one or a combination of several of the following: biomass-based activated carbon, coal-based activated carbon, and petroleum-based activated carbon.

[0065] In some specific embodiments, the specific surface area of ​​the activated carbon is 200–4000 m². 2 / g, particle size 2–100μm (based on D50 diameter), micropores with a pore size less than 2nm and a pore volume of 0.3–0.9cm³. 3 / g, total pore volume is 0.3~1.5cm³ 3 / g. Preferably, the specific surface area of ​​the activated carbon is 800-2000 m² / g. 2 / g, particle size of 6–20 μm (based on D50 diameter), micropores with a pore size of less than 2 nm and a pore volume of 0.45–0.8 cm³. 3 / g, total pore volume is 0.5–1.5 cm³ 3 / g.

[0066] In some specific embodiments, the conductive agent includes one or a combination of several of carbon black, graphene, and graphite.

[0067] In some specific embodiments, the adhesive includes one or a combination of several of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, styrene-butadiene latex, and polyvinyl alcohol.

[0068] In specific embodiments of the present invention, as described above, the proportions of activated carbon, conductive agent, and binder can be: activated carbon 50-93% (mass percentage), conductive agent 2-30% (mass percentage), and binder 5-20% (mass percentage). For example, in some embodiments of the present invention, if 8g of activated carbon, 1g of carbon black (conductive agent), and 1g of polyvinylidene fluoride (binder) are taken, the mass percentages of the three are 80%, 10%, and 10%, respectively.

[0069] In some specific embodiments, the solvent is not particularly limited, as long as it is compatible with the adhesive. For example, in some embodiments of the present invention, if polyvinylidene fluoride is selected as the adhesive, N-methylpyrrolidone and / or dimethylformamide are preferred as solvents.

[0070] In some specific embodiments, the volume ratio of the solvent, activated carbon, conductive agent and binder can be 1:1 to 20:1.

[0071] In some specific embodiments, the solid content of the suspension is 5-50% by volume percentage.

[0072] In some specific embodiments, step (1) specifically includes: weighing activated carbon, conductive agent and binder and placing them in a container, adding solvent to the container, and uniformly mixing and dispersing the solid powder and solvent to form a suspension.

[0073] In some specific embodiments, the uniform mixing and dispersion method includes one or a combination of several of the following: stirring mixing, ultrasonic-assisted mixing, and vacuum-assisted mixing.

[0074] In some specific embodiments, the melamine sponge is impregnated in the suspension using an ultrasonic-assisted impregnation method to make the impregnation more uniform and thorough.

[0075] In some specific embodiments, the melamine sponge is immersed in the suspension for 2 to 30 minutes.

[0076] In some specific embodiments, the mass ratio of the melamine sponge to the activated carbon in the suspension is 1:100 to 1:1000.

[0077] In some specific embodiments, the mass ratio of melamine sponge to its supported activated carbon in the composite precursor is 1:0.5 to 1:10.

[0078] In some specific embodiments, the drying described in step (3) includes freeze drying or oven drying, etc.

[0079] In some specific embodiments, controlling the calcination atmosphere to be an oxygen-free atmosphere includes: placing the composite precursor in a calcination furnace, first using a vacuum system to remove air from the furnace, and then introducing a non-oxidizing gas to completely replace the air in the pores of the composite precursor. Preferably, the non-oxidizing gas can be introduced repeatedly several times.

[0080] In some specific embodiments, the calcining furnace is not limited in form and structure, provided that the required temperature and atmosphere are achieved. For example, in some embodiments, a tubular carbonization furnace, a box-type carbonization furnace, a microwave carbonization furnace, or a vacuum furnace may be used.

[0081] In some specific embodiments, step (4) specifically includes: placing the composite precursor in a calcination furnace, first using a vacuum system to remove air from the calcination furnace, maintaining the pressure inside the calcination furnace at <60 kPa for a period of time, then introducing a non-oxidizing gas, repeating this process several times to completely replace the air in the pores of the composite precursor; after replacement, disconnecting the connection with the vacuum system and cutting off the introduction of the non-oxidizing gas; heating the calcination furnace to reach the constant temperature for calcination and maintaining it for a period of time; after the constant temperature stage ends, cooling the calcination furnace; after cooling, the nitrogen-doped carbon-based composite electrode material is obtained. The purpose of cutting off the introduction of the non-oxidizing gas after replacement (i.e., not introducing gas during calcination) is that during the heating and constant temperature stages, the nitrogen-doped gas released by the thermal decomposition of melamine overflows to the surface of the activated carbon and undergoes a nitrogen-carbon doping reaction at the calcination temperature.

[0082] In some specific embodiments, the non-oxidizing gas includes one or a combination of several of nitrogen, argon, carbon dioxide, and helium.

[0083] In some specific embodiments, the calcination process is preferably controlled using a programmed temperature control system.

[0084] In some specific embodiments, the constant temperature for calcination is 650–950°C, preferably 700–900°C, and more preferably 750–850°C.

[0085] In some specific embodiments, the heating rate of the calcination is 0.5 to 10 °C / min, preferably 1 to 8 °C / min, and more preferably 2 to 5 °C / min.

[0086] In some specific embodiments, the calcination isothermal time is 30–180 min, preferably 60–120 min.

[0087] In some specific embodiments, the cooling is performed using programmed cooling at a rate of 5–10 °C / min. This cooling rate can prevent excessively rapid cooling from damaging the structure of the composite electrode material.

[0088] The second aspect of the present invention provides a nitrogen-doped carbon-based composite electrode material, which is prepared by the above-described method for preparing nitrogen-doped carbon-based composite electrode materials.

[0089] In some specific embodiments, the specific surface area of ​​the nitrogen-doped carbon-based composite electrode material is 500–1500 m². 2 / g, total pore volume is 0.3~1.5cm³ 3 / g, compacted density is 0.15~0.45g / cm³ 3 The nitrogen content in the nitrogen-doped carbon-based composite electrode material is 2.5% to 12% by mass.

[0090] In some specific embodiments, the nitrogen-doped carbon-based composite electrode material has a specific capacitance of 156 F / g or higher in a 6 mol / L potassium hydroxide solution electrolyte at a current density of 1 A / g.

[0091] The technical solutions of the present invention are illustrated in detail below through embodiments and comparative examples. However, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the key points of the present invention.

[0092] The raw materials used in the examples and comparative examples include:

[0093] Activated carbon a: Specific surface area approximately 1600 m² 2 / g, particle size 10-12μm (based on D50 diameter), micropores with a pore size less than 2nm and a pore volume of 0.6cm³. 3 / g, total pore volume is 0.85cm³ 3 / g;

[0094] Activated carbon b: Specific surface area approximately 900 m² 2 / g, particle size 14-20μm (based on D50 diameter), micropores with a pore size less than 2nm have a pore volume of 0.45cm³. 3 / g, total pore volume is 1.2cm³ 3 / g;

[0095] Activated carbon c: Specific surface area approximately 1800 m² 2 / g, particle size 6-10μm (based on D50 diameter), micropores with a pore size less than 2nm have a pore volume of 0.66cm³. 3 / g, total pore volume is 1.06cm³ 3 / g;

[0096] Melamine sponge a: density 8kg / m³ 3 99% open area ratio;

[0097] Melamine sponge b: density 16kg / m³ 3 , with an opening rate of 98%;

[0098] Conductive agent a: Carbon black, purchased from Lion Corporation, Japan, model: CEP600 JD;

[0099] Conductive agent b: Graphene, purchased from Xianfeng Nano Co., Ltd., model: XF021;

[0100] Conductive agent c: Graphite, purchased from Maclean's Reagents Ltd., model: 99.95% METALS BASIS, 8000 mesh;

[0101] Binder a: Polyvinylidene fluoride, purchased from Sinopharm Chemical Reagent Co., Ltd., purity > 95%;

[0102] Binder b: Carboxymethyl cellulose, purchased from Sinopharm Chemical Reagent Co., Ltd., purity > 98%;

[0103] Binder c: Polytetrafluoroethylene, purchased from Sinopharm Chemical Reagent Co., Ltd., purity > 98%.

[0104] The analytical and testing methods used in the examples and comparative examples include:

[0105] 1. Specific surface area, pore volume and average pore size of electrode material: Multi-point BET adsorption method was used, specifically referring to the method described in GB / T19587. For ease of comparison, the specific surface area was measured based on the entire electrode.

[0106] 2. Compacted density of electrode material: Tested according to the method described in GB / T 24533.

[0107] 3. Elemental content analysis of electrode materials: Elemental analysis was performed.

[0108] 4. Electrochemical performance analysis of electrode materials:

[0109] Device assembly: Electrochemical performance was evaluated using a symmetrical dual-electrode capacitor. The active material loaded on the two symmetrical electrodes was of the same mass. A 6 mol / L potassium hydroxide solution was used as the electrolyte. The separator was made of glass fiber (Whatman, GF / D1823-047). The capacitor was assembled using a CR2032 coin cell case.

[0110] Cyclic voltammetry, specific capacitance, and AC impedance testing shall all be performed in accordance with the methods described in IEC 62391-1-2015.

[0111] The specific capacitance (C) is calculated based on the mass of the electrode and follows the formula:

[0112]

[0113] In the formula, I(A) is the discharge current; Δt(s) is the discharge time; m(g) is the mass of activated carbon in the electrode; ΔV(V) is the voltage window of the discharge range, and in the tests of the embodiments and comparative examples of the present invention, ΔV=1.0V.

[0114] Example 1

[0115] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0116] (1) Take 8g of activated carbon a, 1g of conductive agent a (carbon black), 1g of binder a (polyvinylidene fluoride) and 120mL of N-methylpyrrolidone and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0117] (2) Wash and dry the melamine sponge a, then cut it into pieces with dimensions of 2.0cm×2.0cm×0.5cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 10 minutes, the sponge is fully immersed and removed.

[0118] (3) The impregnated sponge is dried at 80°C for 5 hours to remove the solvent and obtain a composite precursor. In the composite precursor, the mass ratio of melamine sponge to activated carbon is about 1:2.5.

[0119] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <60kPa, introduce nitrogen to replace the air in the furnace 3 times, so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the nitrogen supply, raise the temperature to 800℃ at a heating rate of 2℃ / min, maintain this temperature for 120min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with a size of 0.8cm×0.8cm×0.1cm to obtain nitrogen-doped carbon-based composite electrode material, denoted as composite electrode 1.

[0120] The composite electrode 1 has an effective adsorbate (i.e., activated carbon) loading of 2.65 mg and an electrode area of ​​0.64 cm². 2 Therefore, its unit load is 4.14 mg / cm³. 2 The effective adsorbent loading is calculated by subtracting the mass of the material prepared in step (1) without the addition of activated carbon (i.e., Comparative Example 1).

[0121] Figure 2 This is a photograph of the actual composite electrode 1.

[0122] Example 2

[0123] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0124] (1) Take 8g of activated carbon a, 1g of conductive agent a (carbon black), 1g of binder a (polyvinylidene fluoride) and 200mL of N-methylpyrrolidone and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0125] (2) Wash and dry the melamine sponge a, and then cut it into pieces with dimensions of 5.0cm×5.0cm×1.0cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 10 minutes, the sponge is fully immersed and removed.

[0126] (3) The impregnated sponge is dried at 80°C for 5 hours to remove the solvent and obtain a composite precursor. The mass ratio of melamine sponge to activated carbon in the composite precursor is about 1:1.8.

[0127] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <60kPa, then introduce nitrogen to replace the air in the furnace, so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the nitrogen supply, raise the temperature to 750℃ at a heating rate of 2℃ / min, maintain this temperature for 120min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with dimensions of 1.0cm×1.0cm×0.2cm to obtain nitrogen-doped carbon-based composite electrode material, denoted as composite electrode 2.

[0128] Figure 3 The bending resistance of the composite electrode 2 was demonstrated. Figure 3 It can be seen that the composite electrode 2 does not break after being bent at 90 degrees and 150 degrees, and has good self-supporting mechanical properties.

[0129] Figure 4 The compression-resilience properties of the composite electrode 2 are demonstrated. (By...) Figure 4 It can be seen that after being compressed by 200g, the composite electrode 2 can return to its initial state, exhibiting good self-supporting mechanical properties.

[0130] Example 3

[0131] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0132] (1) Take 9g of activated carbon b, 0.2g of conductive agent b (graphene), 0.8g of binder b (carboxymethyl cellulose) and 100mL of water and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0133] (2) Wash and dry the melamine sponge a, then cut it into pieces with dimensions of 2.0cm×2.0cm×0.5cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 25 minutes, the sponge is fully immersed and removed.

[0134] (3) The impregnated sponge is dried at 80°C for 8 hours to remove the solvent and obtain a composite precursor. The mass ratio of melamine sponge to activated carbon in the composite precursor is about 1:3.2.

[0135] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <60kPa, introduce nitrogen to replace the air in the furnace 3 times, so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the nitrogen supply, raise the temperature to 850℃ at a heating rate of 5℃ / min, maintain this temperature for 60min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with a size of 1.5cm×1.5cm×0.1cm to obtain nitrogen-doped carbon-based composite electrode material, denoted as composite electrode 3.

[0136] Example 4

[0137] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0138] (1) Take 6g of activated carbon b, 3g of conductive agent b (graphene), 1g of binder b (carboxymethyl cellulose) and 80mL of water and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0139] (2) Wash and dry the melamine sponge b, then cut it into pieces with dimensions of 2.0cm×2.0cm×0.5cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 5 minutes, the sponge is fully immersed and removed.

[0140] (3) The impregnated sponge is dried at 80°C for 8 hours to remove the solvent and obtain a composite precursor. In the composite precursor, the mass ratio of melamine sponge to activated carbon is about 1:1.3.

[0141] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <60kPa, introduce nitrogen to replace the air in the furnace 3 times, so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the nitrogen supply, raise the temperature to 820℃ at a heating rate of 5℃ / min, maintain this temperature for 90min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with a size of 0.5cm×0.5cm×0.1cm to obtain nitrogen-doped carbon-based composite electrode material, denoted as composite electrode 4.

[0142] Example 5

[0143] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0144] (1) Take 7.5g of activated carbon a, 0.5g of conductive agent c (graphite), 1g of conductive agent a (carbon black), 1g of binder b (carboxymethyl cellulose) and 100mL of water and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0145] (2) Wash and dry the melamine sponge a, then cut it into pieces with dimensions of 3.0cm×3.0cm×0.5cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 5 minutes, the sponge is fully immersed and removed.

[0146] (3) The impregnated sponge is dried at 80°C for 8 hours to remove the solvent and obtain a composite precursor. In the composite precursor, the mass ratio of melamine sponge to activated carbon is about 1:2.2.

[0147] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <60kPa, introduce nitrogen to replace the air in the furnace 3 times, so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the nitrogen supply, raise the temperature to 820℃ at a heating rate of 3℃ / min, maintain this temperature for 60min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with a size of 1cm×1cm×0.1cm to obtain nitrogen-doped carbon-based composite electrode material, denoted as composite electrode 5.

[0148] Example 6

[0149] This embodiment provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0150] (1) Take 8g of activated carbon c, 1g of conductive agent b (graphene), 1g of binder c (polytetrafluoroethylene) and 100mL of N-methylpyrrolidone and add them to a stirring vessel. Stir and mix evenly to obtain a uniform suspension.

[0151] (2) Wash and dry the melamine sponge b, then cut it into pieces with dimensions of 5.0cm×5.0cm×1.0cm. Immerse the melamine sponge completely in the suspension using ultrasonic-assisted immersion. After 3 minutes, the sponge is fully immersed and removed.

[0152] (3) The impregnated sponge is dried at 60°C for 10 hours to remove the solvent and obtain a composite precursor. In the composite precursor, the mass ratio of melamine sponge to activated carbon is about 1:1.6.

[0153] (4) Place the composite precursor in a tube furnace, first use a vacuum system to remove the air in the furnace, maintain the furnace pressure for a period of time to <40kPa, and introduce argon gas to replace the air in the furnace 3 times so that the air in the pores of the composite precursor is completely replaced; after replacement, disconnect from the vacuum system, disconnect the argon gas supply, raise the temperature to 780℃ at a heating rate of 2℃ / min, maintain this temperature for 120min, and then lower it to room temperature at a cooling rate of 5℃ / min. Take out the calcined product, no further processing is required, and directly cut it into electrodes with a size of 1cm×1cm×0.1cm to obtain nitrogen-doped carbon-based composite electrode material, which is referred to as composite electrode 6.

[0154] Comparative Example 1

[0155] This comparative example provides a nitrogen-doped carbon-based electrode material, the preparation method of which is basically the same as that of Example 1, except that no activated carbon is added, and the resulting electrode material is named comparative electrode 1.

[0156] Comparative Example 2

[0157] This comparative example provides an electrode material, the preparation method of which includes the following steps:

[0158] 8g of activated carbon a, 1g of conductive agent a (carbon black), 1g of binder a (polyvinylidene fluoride), and 120mL of N-methylpyrrolidone were added to a stirred tank and stirred until homogeneous to obtain a uniform suspension. A 30cm × 10cm aluminum foil with a thickness of 18μm was taken and uniformly coated onto the aluminum foil using a coating machine, then dried. During the coating process, the coating thickness was adjusted so that the effective adsorbent (i.e., activated carbon) loading per unit area was the same as in Example 1, i.e., 4.14 mg / cm². 2 Then, it was cut into aluminum foil-based electrode material with a size of 0.8cm × 0.8cm, and named control electrode 2.

[0159] Comparative Example 3

[0160] This comparative example provides a nitrogen-doped carbon-based composite electrode material, the preparation method of which includes the following steps:

[0161] 1g of melamine powder and 8g of activated carbon a were uniformly mixed in an appropriate amount of N-methylpyrrolidone and dried. The mixed powder was then placed in a tube furnace. First, the air inside the furnace was evacuated using a vacuum system and maintained at a pressure <60kPa for a period of time. Nitrogen gas was then introduced to replace the air inside the furnace three times. After replacement, the connection to the vacuum system was disconnected, and the nitrogen supply was stopped. The temperature was increased to 750℃ at a rate of 2℃ / min and maintained at this temperature for 120min. Then, the temperature was lowered to room temperature at a rate of 5℃ / min, and the calcined product was removed. The remaining product was then... The calcined product was added to a stirred tank with 1g of conductive agent a (carbon black), 1g of binder a (polyvinylidene fluoride), and 120ml of N-methylpyrrolidone. The mixture was stirred and stirred until homogeneous to obtain a uniform suspension. A 30cm × 10cm aluminum foil with a thickness of 18μm was taken and coated evenly onto the aluminum foil using a coating machine. The foil was then dried. During the coating process, the coating thickness was adjusted so that the effective adsorbent (i.e., activated carbon) loading per unit area was the same as in Example 1, i.e., 4.14mg / cm². 2 Then, it was cut into aluminum foil-based electrode material with a size of 0.8cm × 0.8cm, and named control electrode 3.

[0162] Test case

[0163] The electrode materials of Examples 1-6 and Comparative Examples 1-3 were tested for specific surface area, pore volume, and average pore size, compaction density, nitrogen content, and electrochemical performance. The results are shown in Table 1 below. Figures 5-7 As shown. Figure 5 Linear cyclic voltammetry curve of the capacitor assembled with the composite electrode 1 provided in Example 1. Figure 6 The AC impedance spectrum of the composite electrode 1 assembly provided in Example 1. Figure 7 Adsorption-desorption isotherms of the composite electrode 1 provided in Example 1 and the comparative electrode 2 provided in Comparative Example 2.

[0164] Table 1

[0165]

[0166] A comparison of Comparative Example 1 with Examples 1-6 shows that Comparative Example 1, lacking activated carbon, has an extremely low specific surface area, resulting in lower capacity. The nitrogen-doped carbon-based composite electrode materials provided in Examples 1-6 exhibit specific capacitances exceeding 156 F / g in a 6 mol / L potassium hydroxide electrolyte solution at a current density of 1 A / g, with Example 6 reaching 188 F / g; while Comparative Example 1, under the same testing conditions, has a specific capacitance of only 32 F / g. Furthermore, the electrode of Comparative Example 1 retains less nitrogen. However, due to the three-dimensional porous structure of the melamine sponge, the electrode of Comparative Example 1 exhibits higher ion transport efficiency, meaning that its capacity retention rate at a charge / discharge current of 20 A / g is still significantly higher than that of the electrodes prepared using conventional methods in Comparative Examples 2 and 3.

[0167] By comparing Comparative Example 2 with Examples 1-6, it can be seen that the electrode prepared by the coating method using conventional metal foil in Comparative Example 2 has a lower overall specific surface area than that in Example 1. Due to the absence of nitrogen doping, its capacity is lower than that in Example 1. At the same time, the rate performance (i.e., capacitance retention rate under high current) of the electrode prepared by conventional coating in Comparative Example 2 is about 20% lower than that of the three-dimensional electrode composed of melamine sponge and activated carbon in Example 1. This also shows that the composite electrodes of Examples 1-6 have higher mass transfer efficiency. Figure 7 The difference in mass transfer efficiency between Example 1 and Comparative Example 2 was revealed from the perspective of pore structure. Figure 7 It can be seen that the composite electrode 1 of Example 1 has a larger hysteresis area and a larger adsorption increment at a relative pressure of 0.2-1.0, indicating more mesopores in its electrode structure, especially with a significant adsorption increment in the relative pressure range of 0.9-1.0, which is attributed to the pores formed between the melamine sponge skeleton and the activated carbon particles.

[0168] A comparison of Comparative Example 3 with Examples 1-6 shows that while Comparative Example 3 uses a conventional nitrogen source for electrode preparation, achieving nitrogen doping, its doping level, specific surface area, and capacity still cannot reach the electrode levels of the embodiments of this invention. Most importantly, the electrode material prepared with a common nitrogen source remains a powder structure, relying on coating it onto a metal current collector to function as an electrode. This means it naturally cannot provide self-supporting capabilities or the unique high-efficiency mass transfer capabilities of melamine sponge (the specific capacitance retention rate of Comparative Example 3 is significantly lower than that of Examples 1-6). Furthermore, based on Comparative Example 3, using other known nitrogen sources, such as urea, also fails to achieve the superior performance of the embodiments of this invention because it lacks the special structure of the melamine sponge.

[0169] In summary, this invention achieves a high nitrogen doping level through a relatively simple preparation method, while also realizing self-support of the electrode and improving mass transfer efficiency.

[0170] The nitrogen-doped carbon-based composite electrode material provided by this invention can be used as a self-supporting electrode in energy storage and conversion devices, such as supercapacitors, lithium-sulfur batteries, lithium-ion batteries, sodium-ion batteries, lithium-ion capacitors, sodium-ion capacitors, potassium-ion capacitors, and capacitor deionization devices.

Claims

1. A method for preparing a nitrogen-doped carbon-based composite electrode material, comprising the following steps: immersing melamine sponge in a suspension formed by mixing activated carbon, conductive agent, binder and solvent, drying the melamine sponge after immersion, to obtain a composite precursor; calcining the composite precursor in an anaerobic atmosphere, and obtaining the nitrogen-doped carbon-based composite electrode material after cooling; wherein, based on the total mass of the activated carbon, conductive agent and binder being 100%, the amount of the activated carbon is 50-93%, the amount of the conductive agent is 2-30%, and the amount of the binder is 5-20%; the mass ratio of the melamine sponge to the activated carbon in the suspension is 1:100-1:1000.

2. The production method according to claim 1, wherein The density of the melamine sponge is 4-20 kg / m 3 The open porosity is 95-99.8 %.

3. The method of making according to claim 1, wherein, The activated carbon has a specific surface area of 200 to 4,000 m 2 / g, a particle size of 2 to 100 μm, and a micropore volume of 0.3 to 0.9 cm 3 / g, a total pore volume of 0.3 to 1.5 cm 3 / g.

4. The production method according to claim 1 or 3, wherein The activated carbon has a specific surface area of 800 to 2,000 m 2 / g, a particle size of 6 to 20 μm, a micropore volume of 0.45 to 0.8 cm 3 / g for pores having a diameter of less than 2 nm, and a total pore volume of 0.5 to 1.5 cm 3 / g.

5. The production method according to claim 1, wherein the conductive agent comprises one or a combination of carbon black, graphene and graphite.

6. The production method according to claim 1, wherein the binder comprises one or a combination of polyvinylidene fluoride, carboxymethyl cellulose, polytetrafluoroethylene, butyl rubber latex and polyvinyl alcohol.

7. The production method according to claim 1, wherein the solid content of the suspension is 5-50% by volume.

8. The production method according to claim 1, wherein the activated carbon, conductive agent, binder and solvent are uniformly mixed and dispersed to form the suspension, and the uniform mixing and dispersion method comprises one or a combination of stirring mixing, ultrasonic-assisted mixing and vacuum-assisted mixing.

9. The production method according to claim 1, wherein ultrasonic-assisted immersion is used to immerse the melamine sponge in the suspension.

10. The production method according to claim 1, wherein, the time for immersing the melamine sponge in the suspension is 2-30 min.

11. The production method according to claim 1, wherein in the composite precursor, the mass ratio of the melamine sponge to the activated carbon is 1:0.5-1:

10.

12. The method of producing according to claim 1, wherein, the method for controlling the atmosphere of the calcination to be an anaerobic atmosphere comprises placing the composite precursor in a calcination furnace, using a vacuum system to remove air in the calcination furnace, and then introducing a non-oxidizing gas, so that the air in the pores of the composite precursor is completely replaced.

13. The production method according to claim 12, wherein the non-oxidizing gas comprises one or a combination of nitrogen, argon, carbon dioxide and helium.

14. The method of producing according to claim 1, wherein, no gas is introduced during the calcination.

15. The method of producing according to claim 1, wherein, the constant temperature of the calcination is 650-950 ℃.

16. The method of producing according to claim 1, wherein, the heating rate of the calcination is 0.5-10 ℃ / min.

17. The method of making of claim 1, wherein, the constant temperature time of the calcination is 30-180 min. 18.A nitrogen-doped carbon-based composite electrode material prepared by the method for preparing a nitrogen-doped carbon-based composite electrode material according to any one of claims 1-17.

19. The nitrogen-doped carbon-based composite electrode material of claim 18, wherein, The specific surface area of the nitrogen-doped carbon-based composite electrode material is 500-1500 m 2 / g, and the total pore volume is 0.3-1.5 cm 3 / g, and the compaction density is 0.15-0.45 g / cm 3 The mass content of nitrogen element in the nitrogen-doped carbon-based composite electrode material is 2.5-12 %. 20.The nitrogen-doped carbon-based composite electrode material according to claim 18 or 19, used as a self-supporting electrode in an energy storage and conversion device.

21. Use according to claim 20, wherein, the energy storage and conversion device comprises one or a combination of supercapacitors, lithium-sulfur batteries, lithium-ion batteries, sodium-ion batteries, lithium-ion capacitors, sodium-ion capacitors, potassium-ion capacitors and capacitive deionization devices.

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